Field of the Invention
Embodiments of the present invention relate generally to a multi charged particle beam writing apparatus and a multi charged particle beam writing method, and more specifically, to a method of reducing errors of beam irradiation time in performing multi-pass writing with multi-beams, for example.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits progressively narrows year by year. An electron beam writing technique intrinsically having high resolution is used for writing or “drawing” a mask pattern on a mask blank with electron beams.
As an example employing the electron beam writing technique, a writing apparatus using multi-beams can be cited. Compared with the case of writing a pattern with a single electron beam, since in multi-beam writing it is possible to irradiate multiple beams at a time, the throughput can be greatly increased. For example, in a writing apparatus employing a multi-beam system, multi-beams are formed by letting portions of an electron beam emitted from an electron gun pass through a corresponding hole of a plurality of holes in the mask, blanking control is performed for each beam, each unblocked beam is diminished by an optical system to reduce a mask image and deflected by a deflector so as to irradiate a desired position on a target object or “sample”.
Regarding the multi-beam writing, it is required to be highly accurate and highly speedy. To achieve the high accuracy, it is required to make the error between a desired dose and an actual irradiation dose small. As factors of cause generating the error of the dose, there can be cited the irradiation time resolution of irradiation time data, the performance of a deflector used for blanking control, and so on. When the irradiation time per shot of each beam is defined by n-bit data, the resolution of the irradiation time is defined by the value obtained by dividing the maximum irradiation time per shot by a grayscale value definable by n bits. Therefore, in order to make the error of the dose small, it is necessary to make irradiation time resolution small.